Heavy medium separation media and process



United States Patent 3,297,158 HEAVY MEDIUM SEPARATION MEDIA AND PROCESS Lester B. Anthes, Niagara Falls, Ontario, Canada, assignor to The Carborundum Company, Niagara Falls, N.Y.,

a corporation of Delaware Filed Dec. 30, 1963, Ser. No. 334,259 4 Claims. (Cl. 209-172.5)

The invention of the present application relates to separation media of the type used in sink-float processes.

It is particularly concerned with the preparation of novel separation media and solid constituents thereof and with processes for producing and using such media.

In recent years there has developed considerable interest and activity with respect to gravity separation processes for ores and the like in \which the heavy medium used for separating the relatively light and heavy portions of a feed material comprises a liquid suspension of particles of a solid of high specific gravity. The liquid constituent of the suspension is usually water and among the most useful and widely used materials employed as the solid constituent of such media is ferrosilicon.

Preferably the ferrosilicon used in separation media has a silicon content ranging between about 11 percent and 22 percent by weight, since within that range of composition the ferrosilicon has a high magnetic susceptibility and a relatively high resistance to corrosion and rusting. Thus the solid constitutent of the separation medium may be easily recovered by magnetic means and there is not only little, if any, contamination of the products by corrosion products but also substantially no loss of the ferrosilicon by corrosion. The ferrosilicon may and often will contain up to about percent of other metals as minor constituents since there is no particular advantage to highly pure alloys. As an example of a ferrosilicon product that is quite satisfactory is one which showed on analysis: Fe, 77 percent; Si, percent; Al, 2 percent; Ti, 4 percent; other, 2 percent. Another useful material for use as the solid constitutent of suspension media is the mineral magnetite which like ferrosilicon can be readily recovered by magnetic means.

It is an object of the present invention to provide novel and improved separation media in which a particulate material having high magnetic susceptibility is the solid constitutent.

More specifically it is an object of the invention to provide a particulate ferrosilicon product with which separation media of very high specific gravity and very low consistency may be prepared.

Another object of the invention is to provide a ferrosilicon product of novel shape characteristics which is particularly suitable for use in separation media.

Still another object of the present invention is to provide improved separation processes that utilize ferrosilicon separation media of the character described.

Another object of the invention is to provide a process for producing particulate materials having shape characteristics that make possible separation media having very high densities and very low consistency.

Other objects and advantages of the present invention wil be apparent from the following description thereof, taken in conjunction with the accompanying drawings in which:

FIGURES 1 and 2 are graphical comparisons of the ticle size samples were then determined.

3,297,,i58 Patented Jan. 10, 1957 consistency-specific gravity relationship of novel separation media according to the present invention and previously known media.

Heretofore in separation media for use with such heavy feed materials as metallic ores, ferrosilicon has generally been employed as the solid constituent along with water as the liquid constituent. The specific gravity of such a separation medium is adjusted as necessary to produce proper separation with a specific ore by increasing or decreasing the amount of ferrosilicon used, i.e., by changing the ratio of ferrosilicon to water. Ordinary milled ferrosilioon has been limited in usefulness by the rapidly increasing viscosity of the media in the higher ranges of specific gravity. This viscosity increase hinders settling of the heavier portions of the feed and slows down the separation. For some time there. has been available ferrosilicon atomized from the molten state to form substantially globular particles having smooth, fused surfaces. This product has operated successfully in separation media but is rather expensive. Moreover, the attainment of very high specific gravities in suspensions that contain substantial proportions of the larger atomized ferrosilicon particles is ditficult because these larger particles tend to be porous or hollow and thus have a low bulk density.

Unexpectedly it has been found possible to prepare, inexpensively and without atomization, granular ferrosilicon that not only has a high bulk density but, when mixed with water, also produces suspension media with low viscosities. This result is obtained by subjecting standard, graded, crushed ferrosilicon products to a mulling procedure for a short time.

The resulting novel products have been carefully tested and it has been found that bulk densities in the same range as those of the previously known, atomized ferrosilicon can be easily obtained. It has also been found that in Water suspension the novel, rough-surfaced, mulled ferrosilicon products of the present invention have a relation of suspension viscosity or consistency to suspension specific gravity that is very close to that of suspensions of the smooth, atomized ferrosilicon.

In the following example there is set forth a preferred procedure for producing a novel ferrosilicon product useful for the solid constituent of a separation medium.

EXAMPLE 1 A batch of 2700 lbs. of ground ferrosilicon particles was placed in the pan of a large pan mill and mulled with a heavy roller which was repeatedly passed over the particles. After 15 minutes of mulling a sample was removed for test. Additional test samples were thereafter removed on the completion of 30 and 60 minutes of mulling. Each of these samples, as well as a sample of the unmulled granular ferrosilicon, was independently screened to obtain a separation of particles of different sizes. Controlled particle size samples corresponding to the original samples were then made up by combining for each sample particles of different sizes in such proportions as to obtain in each case a screen analysis as follows: on 65 mesh, 2.0 percent; on mesh, 15.1 percent; on mesh, 15.1 percent; on 200 mesh, 25.2 percent; on 325 mesh, 29.6 percent; through 325 mesh, 13.0 percent. The bulk densities of these controlled par- These are set forth in the following table.

TABLE A TABLE B Sample Time of Malling, Bulk Density, Avg. Avg. Axial Ratio,

minutes g./ec. Material Length, Width, LengthzWidth IHICIODS lTllClOl'lS 3.042 5 15 3. 572 Unmulled 166 78 2. 1 30 3. e32 lviulled min.) 147 79 1. 86: 1 so 3. 684 Mulled (60 min.) 142 78 1. 83:1

Separation media prepared by forming suspensions in 10 To reduce the variable factors the determinations in ater of a number of granular ferrosilicon samples were Table B were made on the fractions of the materials that sted to determine their consistencies :at various specific passed a 170 mesh screen and were held on a 200 mesh ravities. FIGURE 1 of the drawings shows the relation screen. It will be observed in the table that the average :tween the consistency in centipoises and the specific particle width is essentially the same in all cases while the ravity of water suspensions of the controlled particle size 15 average particle length is materially reduced in the mulled imples listed in Table A as determined at 25 C. with samples. It is evident, therefore that the fines are not inpparatus of the type described in Bureau of Mines Report creased unduly by mulling. This is substantiated by other f Investigations 3469-R, dated May 1940. The curves tests in which it was found that after 60 minutes mulling a ranked A, B, C, and D are those representing the correproduct having originally 24.2 percent passing a 325 mesh pondingly identified samples. The curve marked F is screen had only 36.1 percent of the mulled product passnown for comparison and represents the consistencying a 325 mesh screen. It has been found that mulled pecific gravity relation of a water suspension of the ferrosilicon with an average axial ratio of not more than tomized, fused ferrosilicon roduct referred to above. about 1.911 and a bulk density of at least 3.5 g./ cc. is very he sample of this product tested was adjusted in particle satisfactory (other factors being alike) as the solid inize to have the same screen analysis as samples A, B, C, gredient of suspension media. nd D. It will be seen that the media formed from It will be apparent that by the present invention there is ample F is only slightly lower in specific gravity than provided a novel, inexpensive, but quite useful solid conhe media using mulled samples B, C, and D at constituent for separation media and improved separation istencies of from 2 to 25 centipoises while with sample A procedures. While the rocedure set forth above is preunmulled) the consistency of the media increases so ferred for preparing such solid constituents other methods apidly with increasing specific gravity that the suspenof achieving the desired properties and characteristics may ions with higher gravities are not feasible for use. in some instances be employed.

FIGURE 2 of the drawings sets forth a set of curves Unless otherwise indicated percentages specified herein imilar to those of FIGURE 1 which show the relation at are percentages by weight. The sieves or screens used '.5 C. of specific gravity to consistency in centipoises of were U.S. standard sieves. lqueous suspensions of three additional samples of partic- I claim: ilate ferrosilicon, as determined on apparatus of the type 1. A suspension medium which consists essentially of mentioned above. In each sample, the ferrosilicon had a water and particles of ferrosilicon, said particles being .creen analysis of: on 48 mesh, 0.0 percent; on 65 mesh, solid and dense and having a rough, unfused surface, said l.8 percent; on 100 mesh, 7.8 percent; on 150 mesh, 8.2 ferrosilicon having a bulk density of at least 3.5 g./cc. and Jefcent; 011 200 mesh, p on 325 mesh, 133 said medium having at a consistency of 15 centipoises, a iercent; through 325 mesh, 53.4 percent. The curve spgcific gravity greater h 33 narked A shows the results of tests on separation media 2 A Suspension medium as Set f th in claim 1 which formed with regular, granular, unmulled ferrosilicon. has a ifi gravity i th range from about 3.5-3.9 The curve marked B shows that the consistency at high g/Cc.

;pecific gravities of suspensions of granular ferrosilicon A Suspension medium as Set forth in claim 1 in mulled for 105 mmutes 18 {mm lmprmled The Curve which the ratio of average particle length to average parnarked F shows corresponding results with aqueous susticle width is not more than about 1.9.

pensions of used, atomized ferrosilicon particles. It will A A f 3e noted that in these tests, where the granular ferrosilicon 50 I prqcess 1 mmturepf Sohds of (hfemployed has a considerably increased percentage of fine i speclfic gravltls a P frame and f heavy particles, there is little difference between curves B and P fmFtlon Winch 9 formmg bath fluid Sepa' but that both Show a great improvement Over the regular ration medium, said medium consisting essentially of water product represented by Curve For example at a com and particles of ferrosilicon that are solid and dense and sistency of 15 centipoises a specific gravity of about 3.9 are Chamcteriled y 21 Tough, unfused Surface, Said ferrocan be obtained with suspensions of both the mulled prod- SiliCOIl having a bulk density 0f at 1685i ai n uct and the fused, atomized product. On the other hand said medium having at a consistency of 15 centipoises, a with separation media formed from ordinary ground ferspecific gravity of about 3.53.9, introducing said mixture rosilicon to obtain a specific gravity of even 3.2 neccs- I onto said medium, separating the said light fraction to- Sltiltes Teaching a Viscosity of 20 more Cenlipoises- 6O gether with a small amount of medium and subsequently It Will be pp from thfi foregoing that mulling for separating said heavy fraction from the remainder of said even a few minutes is effective in increasing the bulk denmediunL sity of the granular ferrosilicon and decreasing the con- References Cited by the Examiner sistency of separation media made therewith. As shown, continued mulling causes further improvement. However, UNITED STATES PATENTS the improvement is achieved at increasingly lower rates 11, 22 191 9 1942 d 209 and it is therefore not usually feasible to employ a mulling 1 10 222 9 1914 Morat 241 1 7 time of Over one hour- 2,774,734 12/1956 Rodis 252-60 The effect of the mulling is to break down the sharper particles of ferrosilicon thereby increasing the percentage OTHER REFERENCES of particles with blocky shapes. This is shown by the fact Taggart: Handbook of Mineral Dressing, John Wiley & that the average length-width axial ratios of particles of Sons, New York, N.Y., 1945. granular ferrosilicon are much less after mulling than be fore. This is set forth in the following table. FRANK W. LUTTER, Primary Examiner. 

4. A PROCESS FOR SEPARATING A MIXTURE OF SOLIDS OF DIFFERENT SPECIFIC GRAVITIES INTO A LIGHT FRACTION AND A HEAVY FRACTION WHICH COMPRISES FORMING A BATH OF A FLUID SEPARATION MEDIUM, SAID MEDIUM CONSISTING ESSENTIALLY OF WATER AND PARTICLES OF FERROSILICON THAT ARE SOLID AND DENSE AND ARE CHARACTERIZED BY A ROUGH, UNFUSED SURFACE, SAID FERROSILICON HAVING A BULK DENSITY OF AT LEAST 3.5G./CC., AND SAID MEDIUM HAVING AT A CONSISTENCY OF 15 CENTIPOISES, A SPECIFIC GRAVITY OF ABOUT 3.5-3.9, INTRODUCING SAID MIXTURE ONTO SAID MEDIUM, SEPARATING THE SAID LIGHT FRACTION TOGETHER WITH A SMALL AMOUNT OF MEDIUM AND SUBSEQUENTLY 